ICPMS

The Thermo X Series quadrupole ICPMS has a single collector (SEM) that can operate in both analog and pulse counting modes thereby allowing simultaneous analyses of elements that are present in wt% to ppt levels. It is equipped with a collision/reaction cell and is capable of analyzing about 70 elements in any sample that can be put into aqueous solution. Detection limits and analytical precision vary widely with analytical protocol, instrumental response, blank contamination, interferences, matrix composition, and isotope abundance, but ranges from <100 ppb to <1 ppt (parts per trillion) in aqueous solution.

Sample preparation

All users are responsible for dissolving and preparing their own samples.

• Samples must be in aqueous solution, preferably ~1-2% HNO3. Higher HNO3 concentrations can be tolerated, but other acids should usually be avoided unless there is a specific reason for them, or if it is certain that there are no important additional interferences caused by them.
• Total dissolved solids (TDS) in the analytical solution should be <0.1% (1000 ppm), preferably <0.05% (500 ppm).
• For best results, element concentrations in solution should generally be >0.01 ppb. Having element concentrations <10 ppb is desirable as it reduces wear on the detector.
• High-purity reagents and water should be used to keep blanks low.
• Well-characterized standards should be used.

Guidelines for sample preparation

A) For silicate rocks and minerals:

Dissolve ~25 mg of samples using a combination of HF, HNO3 and HCl (sometimes HClO4) acids. When using HF, use Teflon vessels (for e.g. from Savillex, USA). Do not use glass or quartz containers. Si concentrations cannot be measured accurately when samples are treated with HF. Use clean acids with very low analytical blanks. After dissolution, evaporate the acids, add some more nitric to reduce formation of insoluble fluorides. After evaporation, dilute the samples 4000-5000 times. For example, if you dissolved 25 mg of a basalt, the sample after dissolution should be diluted to 100 ml of 2% nitric which can be stored in 125 ml HDPE/LDPE bottles. Carefully weight the initial sample and final solution. This is needed to calculate the dilution factor. Bring at least 10 ml of this diluted sample for analysis.

B) Non-silicate solid samples:

Use a combination of HNO3 and HCl (aqua regia) to dissolve the sample. After evaporation, flux the sample with some more HNO3. The remaining steps are the same as above.

C) If you have carbon in your samples:

Treat the samples first with H2O2 or some other strong oxidizing agent or ash the sample before dissolving in concentrated inorganic acids as above.

D) Water samples:

Weigh enough water sample (must be acidified soon after collection), filter it, add enough nitric acid. Rest of the steps are the same as above.

Choosing internal standards (optional)

Internal standards allow correction for some aspects of instrumental drift. You can choose any internal standard elements you want, but consider the following:

• An internal standard element should not be an element of interest; it should not have an isotope that is the same as an analyzed isotope.
• Avoid internal standard elements having isotope masses 16 less than an analyzed isotope to avoid MO+ oxide interferences.
• Avoid internal standard elements having isotope masses exactly twice the mass of an analyzed isotope to avoid M2+ interferences.
• The concentration of the internal standard element naturally present in your samples should be much lower that that of the internal standard you add.
• The internal standards should be close as possible to the masses of the analyzed elements.

Internal standards typically used are:

• Water samples: Be, Sc, Ga, Y, In, Pr, Re, Bi, Th.
• Rock and mineral samples: Rh, In, Re, Bi.
• Lanthanides only: Cs, Re.

Containers

If possible, all bottles, volumetric flasks, pipettes, and other things that hold the liquid solutions should be made of plastic, not glass. Plastic ware should be thoroughly washed and pre-leached in 20% reagent grade HNO3. Solutions should never be stored in glass.

Reagents

Reagents should preferably be of "high-purity" or "ultra high-purity" grade, not the commonly used "reagent grade". 18 MOhm-cm deionized or double distilled water should be used.

Cleanliness

Although clean room facilities are not strictly necessary for preparation or routine samples, it is extremely important to keep the work area clean, especially free of dust, including dust falling from above. Pre-soaking all containers in 20% reagent grade HNO3 followed by rinsing with high-purity water eliminates many contamination problems. Don't assume new plasticware is free of contamination (e.g., polypropylene test tubes with Pb or Cu and Zn contamination).

Standards and blanks

The user must bring their own standards and acid blanks. Use standards as similar as possible to the unknowns (matrix matching). Because of the linear response of the instrument over 6 to 8 orders of magnitude, use of a blank and one well-characterized standard is possible, though perhaps not wise. It is wise not to use standards having element concentrations vastly different than the unknowns.

Sticky elements

Certain elements are "sticky" in the ICP-MS sample introduction system. Some offenders include Li, B, platinum group elements, Ag, Au, Hg, Nb, and Ta. Some can be rinsed from the sample introduction system by extended (>1 minute) wash times between samples with 10% HNO3. Others can be washed out using different acids or higher acid concentrations. Some require more exotic wash solutions.

Usage charges

All users must fill-up the user form and submit it in advance. The user will be charged based on the number of solutions they analyse. Please refer to the attached document(s) below.

Disclaimer

The preparation of standard and sample solutions is entirely the responsibility of the user. The ICPMS lab is not responsible for problems with data quality related to sample preparation.